Protection of storage tanks for explosive liquids



Nov. 10, 1959 A. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS Filed Oct. 21, 1957 4Sheets-Sheet 1 ATTQRNEYS Nov. 10, 1959 A. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE; LIQUIDS Filed Oct. 21, 1957 4Sheets-Sheet 2 BY I NV ENTOR ATTQRNEW Nov. 10, 1959 Filed Oct. 21, 1957VA. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS 4 Sheets-Sheet 3 J2 'a-2o l l ,/2/ --22 -22 I 22 I 2/\ 2la 2/ l L. 5; My 3/ HLJ/ Q FIG. 4. |-r

Nov. 10, 1959 A MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS Filed Oct. 21, 1957 4Sheets-Sheet 4 United ates atentO PROTECTION OF STORAGE TANKS FOREXPLOSIVE LIQUIDS Anders Mathisen, Alverstoke, England, assignor ofonehalf to Graviner Manufacturing Company Limited, and one-half toWilkinson Sword Limited, both of London, England, both British companiesApplication October 21, 1957, Serial N0. 691,452

Claims priority, application Great Britain October 22, 1956 2 Claims.(Cl. 169-4) This invention relates to fire and explosion protectionsystems.

The invention is particularly applicable to the proter tion of vesselsin which hydrocarbon liquid fuels such as petroleum and other aviationfuels are stored.

Fires and explosions in static petroleum storage tanks are notinfrequent. They may also occur in tankers used for transporting liquidhydrocarbon fuels by road and in fuel bowsers used to carry fuel toaircraft for refuelling. With the latter, apart from normal peacefulhazards, it may be desirable to provide protection against fires orexplosions resulting from enemy action.

One of the problems in protecting fuel storage tanks against fires andexplosion is that the level of liquid in a tank will vary from time totime in dependence upon the amount of liquid withdrawn from the tank.Thus, the means used for distributing fire or explosion suppressant mustfunction satisfactorily quite independently of the level of the liquid.Heretofore, this problem has been tackled, as far as fire protection isconcerned, in many ways. The most usual solution has been to provide asource of fire extinguishing material which can float upon the liquidand thus rise and fall with the level of the liquid in the tank.

The present invention has for its object to provide a novel solution tothis problem, which is effective in suppressing explosions in storagetanks, whilst such explosions are still at the incipient stage, and mayalso be effective in extinguishing fires in the tanks.

The present invention achieves this by providing one or more elongatedcolumns containing explosion suppressant material which is or aremounted vertically to extend at least between the maximum and minimumlevels for liquid in the tank, each column containing at least oneelectrically ignitable explosive charge ignition of which can beeffected by explosion detection means upon the onset of an incipientexplosion in the tank.

Each column may consist of a plurality of individually operable portionsor containers positioned end-torend. In such cases, it may be arrangedthat only those portions or containers which are above the surface ofthe liquid are operated in the event of an explosion. This may beachieved by providing liquid-level operated switches mounted atappropriate levels in the tank and arranging to render non-operablethose parts of a column which are submerged or partly submerged.

The invention will be better understood from a consideration of thefollowing description of two systems for the protection of fuel storagevessels, the first designed for the protection of static fuel tanks andthe second designed for the protection of bowsers or tankers, eachsystem being described as an example only of possible systems inaccordance with the invention.

The systems are illustrated in the accompanying diagrammatic drawings,in which:

Figure 1 is a sectional side elevation of a static fuel tank protectedin accordance with the first system, and

Figure 2 is a sectional plan view of the tank of Figure 1, whilstFigures 3A and 3B show alternative electric circuits for theinter-connection of the components of the first system;

Figure 4 is a sectional side elevation of a mobile fuel bowser or tankerprotected in accordance with the second system, whilst Figure 5 is asectional view taken along the line VV in Figure 4, and

Figure 6 is a detail sectional view of an alternative form ofsuppressant distributor.

Referring now to Figures 1 and 2 these show a static fuel tank 10provided with two incipient-explosion detection means 11 situated on theinside of the roof above the maximum fuel level. The detection means 11may take the form of pressure-rate-of-rise detectors of the kinddescribed in United States Patent No. 2,693,240 and illustrated inFigures 1 and 2 or 10 and 11, or the modified constructions shown inFigures 1 to 3 of United States Patent No. 2,768,261. On the other hand,where conditions are such that a greater rise in pressure is permissiblebefore suppression occurs, it may be possible to use a simple pressureswitch. Alternatively, in order to detect the illumination radiated by apotential ignition source or the incipient explosion flame itself thedetection means 11 may be of photoelectric form as described in thespecification of United States patent application Serial No. 421,302,filed April 6, 1954, now Patent No. 2,869,647, dated January 20, 1959.

For distributing the fire or explosion suppressant material elongatedfrangible suppressant containers 12 are provided. These containers areof the general form described and illustrated in United States PatentNo. 2,787,330, and a number of such containers 12 are mounted end-to-endin a plurality of columns which are positioned vertically to extendbetween the base and roof of the tank 10. As is explained in UnitedStates Patent No. 2,787,330 when the explosive charge in a container 12is ignited, the suppressant material therein is distributed radiallyoutwards in all directions. Thus, by arranging the vertical columns ofcontainers 12 at suitable spacings it can be ensured that the wholevolume of the tank above the liquid is filled with suppressant materialwith suificient rapidity and in a sufiicient concentration to effect Isuppression of an explosion before it has passed the incipient stage, orextinguish a fire if the vapour-air mixture is not of explosiveconcentration.

It will be understood that the detection means 11 are electricallyconnected via a source of electrical power 13 suitably positionedoutside the tank, to the igniters of the explosive charges in thecontainers 12, so that when the detection means 11 are operated by theoccurrence of a fire or explosion they complete a firing circuit for theigniters. A suitable power supply apparatus 13 for use with detectionmeans of the kind in which a pair of electrical contacts are closed, isdescribed and illustrated in United States Patent No. 2,782,402.

With such an arrangement it may be undesirable to explode thosecontainers which are located below the fuel level, in view of the riskof the resultant hydraulic shock damaging the walls of the tank 10. Insuch a case, in accordance with the invention, level switches 14 ofknown form are provided in order to cut out those suppressant containers12 which are submerged, and possibly those containers which are partlysubmerged. These level switches 14 have a float 14a supported by apivotable arm 14b. When the level of the fuel rises above a particularswitch the float 14a rises and pivots the arm 14b which is arranged toclose a pair of electrical contacts in a sealed housing 14c. The closingof these contacts short-circuits the igniters of the explosive chargesof the submerged or partially submerged containers. In this way, allcontainers beneath the liquid are rendered non-operative and only thoselocated above the fuel are operated in the event of a fire or explosion.Instead of being float operated, the disconnecting switches may have theform of a bellows or diaphragm which is moved to close the contacts whenit is submerged.

Figure 3A shows a circuit diagram which makes it clear how the explosivecharge of a container 12 is only supplied with current from the powersource 13 in the event of closure of one or both of the detectorcontacts 11, if the contacts of the level switch 14 at the correspondinglevel are also open because the fuel is below that level.

Alternatively, the circuit of Figure 3B may be employed in which casethe level switches 14 are arranged to open the pair of contacts of aswitch when the float rises, the contacts thereby open-circuiting thecorresponding igniters of the explosive charges.

The second system shown in Figures 4 to 6 is 'designe for the protectionof mobile fuel bowsers or tankers. In this case, two incipient explosiondetectors 20 are mounted on opposite ends of the tank 21. Wherepressure-rate-ofrise detectors of the kind referred to in connectionwith Figures 1 and 2 are used, the contacts of these are connected inseries so that both must be operated in order to effect distribution ofsuppressant. In this way, movement of the fuel to one end of thecontainer, due to its inertia when stopping or starting, will not causeinadvertent operation because only one or the other of the detectors islikely to respond to such fuel movements.

Due tothe fact that the depth of such a tank is usually much less thanthat of a static tank, the suppressors 22 may'in this case be'ofsufiicient length for only one to be used in each of the threecompartments defined by the two apertured bafiles 21a which are providedto limit movement of the fuel in the tank. The construction of thesuppressors 22 may be similar tothat described in United States patentspecification No. 2,787,330, but an alternative construction illustratedin Figure 6' will now be described. In this construction the suppressorconsists of a glass envelope 22a, and the explosive charge 23 is ofknown cord form and is supported in a glass tube 24 extending along theaxis of the envelope 22a. Firing of the charge 23 is initiated by anelectrically-fireddetonatorlS the leads 25a of which are connected tothe terminals of aterminal box 26. The envelope 22a is held against amounting plate 27 by a clamp 28 secured to the mounting plate 26 bythree bolts 29 (only one of which can be seen in this figure). The plate27 is in turn secured across an aperture in the upper surface of thetank 21 by bolts 30. Supports 31 are provided for the lower end of eachsup-v pressor 22.

The suppressors 22 are electrically connected to the detectors 20 to apower supply 32.

What I claim is: r 1. In combination, a plurality of elongated frangibleliquid containers fitted in a closed storage tank for exploliquidoperated electric switches which is located at a level corresponding tothat of the container in which the respective igniting means is mounted.

2. In combination, at least one column of frangible elongated liquidcontainers mounted vertically in a closed storage tank for explosiveliquids, said column consisting of a number of individual containersjoined end-to-end and each containing an explosion suppressant materialand an explosive charge, said explosive charge having electricaligniting means whereby upon ignition of said explosive charge thecontainer is burst and the material therein is dispersed explosiondetection means responsive to an explosion whilst it is still in theincipient state, said detection means having circuit closure means whichis closed upon response of said detection means to an incipientexplosion, a source of electric current, and a number of liquid-levelelectric switches each mounted at a different level in said tank, saidlevel switches being equal in number to the number of individualcontainers and each having contacts which are opened when the liquid inthe tank is at a predetermined level relative to the switch, andelectrical conductors for coupling each igniting means in a separatecircuit with said circuit closure means and said current source and withthat one of said level switches Whose contacts will be opened when thecontainer in which that igniting means is mounted is at least partlysubmerged in the liquid stored in the tank.

' References Cited in the file of this patent UNITED STATES PATENTS

